1. Field of the Invention
The present invention generally relates to the manufacturing of a product using a scheduler for dispatching of lots of products being manufactured to tools and other resources to be used in the manufacturing process and, more particularly, to maximize throughput of all available tools and resources.
2. Description of the Prior Art
The manufacturing of products is a major sector of the economy of many countries of the world and a wide variety of new products are developed and introduced annually. At the present time, developments in technology have led to an increase of average complexity of products while increasing the rate at which products may become obsolete. Therefore, manufacturing infrastructure such as processing pipelines, assembly lines and the like typically comprise tools and resources which are more generalized than in the past such that they can be used to carry out alternative processes and perform many diverse manufacturing operations and can be flexibly applied to the manufacture of products of widely varying types and designs including individually customized and short run products.
Both the complexity of products being manufactured and the complexity and cost of tools and resources used for manufacturing requires sophisticated scheduling, often supported by computers, for allocation of tools (such as semiconductor photolithography cells, numerically controlled machine tools, die or wire bonders, chemical-mechanical polishing devices and the like) and resources (which can include materials, intermediate products, partially processed materials or other instrumentalities such as testing or inspection equipment, data processing system peripherals, software, hardware or firmware and the like) to particular manufacturing processes in order to maintain manufacturing efficiency and to meet manufacturing schedules which are often critical and stringent.
In general, scheduling is often arranged somewhat incrementally for relatively short periods of time (e.g. several minutes, hours, days or weeks) and is performed generally in parallel with a corresponding manufacturing process. That is, the scheduling for allocation of tools and resources will be performed concurrently with execution of scheduled processes but a short period of time in advance of the corresponding manufacturing processes such that scheduling for each short period of manufacturing will be complete by the time each corresponding short period of manufacturing is to begin and determines what tools and resources will be allocated to particular manufacturing processes and workpieces, data or the like for that short period of time.
Tools and resources, of course, are subject to normal wear or needs for periodic maintenance and upgrades as well as being subject to unanticipated damage or malfunctions that require the tools or resources to be taken off-line, sometimes referred to as being “down”. A tool or resource will also be unavailable for a particular process during any period it is allocated to another process. When scheduling for a period of time for a particular process is performed, only tools and resources known to be available at the beginning of scheduling can be allocated to manufacturing processes by the scheduling. Thus, if a previously unavailable tool or resource becomes available after scheduling for a period of manufacturing has begun, it will not be seen as being available until the start of scheduling for the next subsequent period of manufacturing. This delay is referred to as latency and results in the tool or resource not being productively utilized for a period of time and may compromise manufacturing throughput.
To reduce the time a given available tool or resource is not productively utilized, it has been suggested in U.S. Pat. No. 6,907,305 to update the existing schedule to reflect such occurrences. However, such an approach is not efficient or particularly effective since it requires time for modification of an existing schedule and implementation of the modified schedule to include activities associated with inclusion of the tool or resource in the schedule which may already be critical.